The invention relates to a process for preparing fluorine-containing ethane derivatives of the general formula F.sub.k CH.sub.n Cl.sub.3-(k+n) CZ.sup.1 Z.sup.2 F, wherein k, n, Z.sup.1 and Z.sup.2 have the meanings described below.
There is an increasing demand for environmentally compatible halohydrocarbons. Fluorine-containing ethane derivatives which contain at least one hydrogen atom, for example CF.sub.3 CH.sub.3 (R143a), CF.sub.3 CH.sub.2 Cl (R133a) and especially CF.sub.3 CHCl.sub.2 (R123) and CF.sub.3 CH.sub.2 F (R134a), for example, have proved to be such compounds. However, the corresponding 1-fluoro or 1,1-difluoro compounds are also of interest, for example the compounds CFCl.sub.2 CHCl.sub.2 or CF.sub.2 ClCHCl.sub.2, which are regarded as environmentally compatible and can be used as refrigerants, solvents or propellants.
Such compounds are prepared industrially from correspondingly halogenated derivatives by catalyzed halogen/fluorine exchange, particularly by chlorine/fluorine exchange. However, the halogenated starting compounds used here are very slow to react in a halogen/fluorine exchange.
In particular, drastic process conditions are needed to prepare more highly fluorinated compounds. In spite of such drastic conditions, for example working in the gas phase, the conversions are usually low. Another disadvantage of known processes is that the catalysts used, which are often very expensive, do not have a satisfactory life.